Conventionally, there is a known phenomenon that when a liquid is supplied to a surface of a substrate such as a piezoelectric material on which surface acoustic wave is propagated, the liquid receives an energy of the surface acoustic wave, flows and vibrates, and as a result, the liquid changes to microparticles (nanoparticles) and flies. Apparatuses which atomize a liquid by using the above phenomenon are variously suggested. As a principle of atomization, for example, it is described that the surface acoustic wave (Rayleigh wave) which propagates on the surface of the substrate, after getting into the liquid, changes to surface tension wave (capillary wave) which propagates on the surface of the liquid, and as a result, mist is generated from the liquid surface.
The surface acoustic wave in the above atomizer is excited by an application of high-frequency electricity to an interdigital electrode formed on a surface of a piezoelectric substrate. The interdigital electrode, which is an electrical component, needs to be protected from a trouble such as a short circuit or rust deterioration caused by the liquid. Moreover, the liquid needs to be stably guided (fed) and supplied to a predetermined atomizing area at a constant quantity per unit time to atomize the liquid stably with high-energy efficiency. As means for liquid supply, it is considered to use a liquid surface tension or a capillary action.
Although the surface acoustic wave is not used, for example, there is a known spray head which atomizes a liquid by supplying the liquid to a surface of a discoid vibration plate which produces ultrasonic vibration of longitudinal vibration mode (refer to patent document 1, for example). In the above spray head, the liquid is supplied through an annular gap which is formed with a folded part of a cylindrical tube closely positioned to a periphery of the vibration plate, and a thickness of the liquid film is held by a surface tension of the liquid.
Moreover, there is a known atomizing apparatus provided with a piezoelectric substrate which has an interdigital electrode to excite surface acoustic wave on its surface, a spacer which is disposed around the edge of the surface of the piezoelectric substrate, and a liquid supply plate which has an outlet of mist and disposed facing the surface of the piezoelectric substrate across the spacer, and those make up a space to hold a liquid (refer to patent document 2, for example). In this atomizing apparatus, the liquid is supplied to above-mentioned space by a capillary action in a liquid leading passage communicated with the space.